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FreeBSD-EN-17:07.vnet                                           Errata Notice
                                                          The FreeBSD Project

Topic:          VNET kernel panic with asynchronous I/O

Category:       core
Module:         kernel
Announced:      2017-08-10
Credits:        Kristof Provost
Affects:        FreeBSD 11.0 and later.
Corrected:      2017-07-28 18:09:41 UTC (stable/11, 11.1-STABLE)
                2017-08-10 06:59:07 UTC (releng/11.1, 11.1-RELEASE-p1)
                2017-08-10 06:59:26 UTC (releng/11.0, 11.0-RELEASE-p12)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

POSIX asynchronous I/O permits applications to request asynchronous
completion of I/O requests.  VNET permits systems to be configured
with multiple instances of the in-kernel network stack.

II.  Problem Description

The implementation of POSIX asynchronous I/O for sockets completes I/O
requests in a pool of dedicated worker threads.  The VNET feature requires
threads to explicitly select an active instance of the network stack before
performing network operations.  The function used to complete asynchronous
I/O requests was not setting a network stack instance before completing I/O
requests.

III. Impact

Using POSIX asynchronous I/O with sockets in a VNET-enabled kernel will
panic.

IV.  Workaround

No workaround is available, but systems that do not enable VNET via a
custom kernel are not affected.

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

Afterward, reboot the system.

2) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Recompile any custom kernel configs using VNET.

Afterward, reboot the system.

3) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-17:07/vnet.patch
# fetch https://security.FreeBSD.org/patches/EN-17:07/vnet.patch.asc
# gpg --verify vnet.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/11/                                                        r321657
releng/11.0/                                                      r322343
releng/11.1/                                                      r322342
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-17:07.vnet.asc>
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